I have a separate file for my navbar, which I load into the main file using the method from the first answer here. However when I now try to select the elements from the navbar, I get a null reference error. How can I solve this?
index.html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" href="../style.css">
    <link rel="stylesheet" href="blog.css">
    <title>My name</title>
    <link rel="preconnect" href="https://fonts.googleapis.com"> 
    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin> 
    <link href="https://fonts.googleapis.com/css2?family=Montserrat:wght@100&display=swap" rel="stylesheet">
    <script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
    <div id="nav-placeholder">
    </div>
    <script>
    $(function(){
      $("#nav-placeholder").load("nav.html");
    });
    </script>
    <script src="app.js"></script>
</body>
app.js
const navSlide = () => {
    const burger = document.querySelector('.burger');
    const nav = document.querySelector('.nav-links');
    const navLinks = document.querySelectorAll('.nav-links li');
burger.addEventListener('click',()=>{
    //Toggle Nav
    nav.classList.toggle('nav-active')
    //Animate Links
    navLinks.forEach((link, index)=>{
        if (link.style.animation){
            link.style.animation = '';
            // link.style.animation = `navLinkFadeOut 0.5s ease forwards ${index / 7 + 0.2}s`;
        } else {
            link.style.animation = `navLinkFadeIn 0.5s ease forwards ${index / 7 + 0.2}s`;
            }        
        })
    });
}
const app = ()=>{
    navSlide();
}
app();`
 
    